1. Field of the Invention
The present invention relates to a hybrid vehicle control apparatus that controls an engine that rotates at least one first wheel and an electric motor that rotates at least one second wheel that is mechanically independent from the engine. More particularly, the present invention relates to stabilizing the vehicle driving performance when there is a change in the portion of the total drive torque of the first and second wheels that should be carried by the engine.
2. Background Information
A four-wheel drive type vehicle control apparatus is well known that drives both the first wheels (e.g., rear wheels) and the second wheels (e.g., front wheels) with an engine. This kind of traditional 4WD system uses a transfer mechanism that includes a multiple disk clutch mechanism to distribute the engine drive torque between the front and rear wheels. Consequently, the total drive torque is held constant even if the distribution ratio of the drive torque changes.
In recent years a hybrid 4WD system has been proposed (see Japanese Laid-Open Patent Publication No. 8-300965) which rotates one set of wheels with an engine and rotates the other set of wheels with an electric motor. In this system, there is no mechanical connection between the front and rear wheels. Rather, the drive torque that is transmitted to each set of drive wheels must be adjusted relative to each other in order to keep the total drive torque constant. This presents new problems in terms of driveability.
In view of the above, there exists a need for an improved hybrid vehicle control apparatus that overcomes the problems of the prior art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
Generally, the engine is advantageous over the electric motor in terms of output but disadvantageous in terms of response. As a result, several problems arise. For example, consider a case where the drive force distribution with respect to the front wheels and rear wheels changed (from a state where 100% of the drive torque is transmitted to the rear wheels to a state where 50% of the drive torque is transmitted to the front wheels as well as to the rear wheels) due to slippage or the like. If the engine and electric motor are made to converge on their respective target drive torques, which correspond to the drive force distribution, in an unrelated manner, the drive torque of the electric motor will increase quickly while the drive torque of the engine will require a considerable amount of time to decrease. Consequently, the total drive torque will increase temporarily and a feeling of acceleration will occur.
Meanwhile, if one considers a case where the drive system is shifted from 4WD to 2WD, in which only the engine driven wheels are driven, the drive torque of the electric motor will vanish quickly while the drive torque of the engine will require a considerable amount of time to rise. Consequently, the total drive torque will decrease temporarily and a feeling of speed loss will occur.
In view of these actual circumstances, the object of the present invention is to provide a hybrid vehicle control apparatus that can prevent the aforementioned degradation of driving performance that occurs when the drive force distribution is changed by controlling the torque of the electric motor so as to match the response of the engine.
Therefore, in accordance with one aspect of the present invention, a hybrid vehicle control apparatus is provided for a vehicle having front and rear wheels with at least one of the front and rear wheels being an engine driven wheel driven by an internal combustion engine and at least one of the front and rear wheels being a non-engine driven wheel driven by an electric motor that is mechanically independent from the engine. The hybrid vehicle control apparatus basically comprises a total target drive torque setting section, a target engine torque setting section, and a motor command value setting section. The total target drive torque setting section is configured to set a total target drive torque of the engine driven wheel and the non-engine driven wheel. The target engine torque setting section is configured to set a target engine torque, which is portion of the total target drive torque that should be produced at the engine driven wheel. The motor command value setting section is configured to set a torque command value for the electric motor in a delayed manner with respect to a change in the target drive torque of the electric motor when the target engine torque changes. The torque command value corresponds to a distribution ratio of the total target drive torque that should be produced at the non-engine driven wheel.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.